1. Field of the Invention
The present invention relates to a flame-retardant epoxy resin composition formed by mixing flame-retardant particles to an epoxy resin, and an electronic device, a laminated circuit board, a multilayered circuit board and a printed circuit board using the flame-retardant epoxy resin composition.
2. Description of the Related Art
Resin compositions containing an epoxy resin, which is a thermosetting resin having good mechanical strength, electrical characteristics, chemical resistance, etc., have been used in sealing materials for sealing ICs and LSIs, in laminated circuit board, in multilayered circuit boards, and in printed circuit boards. In order to add flame resistance to resin compositions containing an epoxy resin, flame-retardant agents such as brominated epoxy resin have been conventionally added to the resin compositions.
However, although halogen based flame-retardant agents such as brominated epoxy resin exhibit superior flame retardancy, they might produce harmful brominated dioxines through thermal decomposition of the halogen based flame-retardant agents. Therefore, various flame-retardant agents for replacing the halogen based flame-retardant agents have been studied.
Typical examples of flame-retardant agents that replace the halogen based flame-retardant agents are metal hydroxides (metal hydrates), as described in Japanese Patent Application Laid-Open (JP-A) Nos. 2002-30200, 2003-192874, 2001-323169 and 2003-64185. In a case where a metal hydrate is mixed in an epoxy resin, it is preferred to form a uniform coating layer on surfaces of particles of the metal hydrate so as to improve dispersibility of the particles in the epoxy resin and to prevent deterioration of resin characteristics due to an active group included in the metal hydrate affecting the epoxy resin. Known methods for surface treatment of metal hydrate particles include treating, for example, with a higher fatty acid, forming a silica layer, and the like. However, it is difficult to sufficiently disperse the particles under conventional reaction conditions, and a rate of coating reaction is fast. Therefore, there is a problem in that the particles are subjected to the coating reaction in an aggregated state, whereby uniform coated particles cannot be obtained.
In addition, if the surface treatment is insufficient, humidity resistance of the epoxy resin composition is deteriorated, and the epoxy resin may have poor solder crack resistance.
Further, since flame retardancy of the metal hydrates is lower than that of the halogen based flame-retardant agents, it is necessary to blend a large amount of metal hydrate in the resin to obtain necessary flame resistance. However, if a large amount of metal hydrate is blended in the resin, problems arise such as deterioration of dynamic performances of the resin and lowering of moldability of the resin.